The invention relates to an active part of an electrical machine comprising teeth, each of which has a tooth base and a tooth height, open or closed slots which are arranged between the teeth, and windings which are introduced into the slots and surround at least one of the teeth in each case, wherein starting from the outer surface of the respective tooth bases and in extension of the teeth, the active part has an active part thickness which is greater than the tooth height, wherein starting from the respective tooth base and extending to a limit depth which is at most equal to the tooth height, the active part comprises a first material having a first magnetic permeability and, beyond said limit depth, comprises a second material having a second magnetic permeability, wherein the first magnetic permeability is greater than the second magnetic permeability. The invention further relates to such an electrical machine, to a radial magnetic bearing comprising such an active part, and to a method for producing such a radial magnetic bearing.
Electrical machines may be embodied e.g. as motors, such as linear motors and rotor-based motors, as generators, or as magnetic bearings, in particular radial magnetic bearings.
Such an active part may be used in the case of e.g. an active radial magnetic bearing which comprises a stator and a rotor. The stator usually consists of a laminated core with a plurality of coils. These coils generate a magnetic field which exerts a dynamic effect on the rotor. The force density that can be achieved in this way depends inter alia on the square of the magnetic flux density. In order to construct a compact magnetic bearing, it must be possible to generate a maximum flux density. The maximum flux density is limited by the material properties of the laminate material that is used. Magnetic bearings are usually operated using magnetic flux densities in the range of 1.2 to 1.5 Tesla.
One known means of increasing the magnetic flux density is the use of laminate materials made from cobalt-iron alloys (Co—Fe alloys). This allows flux densities of up to 2 Tesla to be achieved, corresponding to approximately twice the force density. One disadvantage of this solution is the material cost, which is very high in comparison with standard sheets. Moreover, the cobalt-iron sheet is only available in dimensions which require segmentation to be used in the case of large magnetic bearings, e.g. having diameters greater than 300 mm.
In order to allow for the configuration of machines having internal armatures, dynamo-electric rotor-based machines and radial magnetic bearings often have laminated stators featuring slots which are arranged between teeth that point radially inwards, and winding systems such as e.g. chorded windings or tooth-wound coils which are positioned within said slots. The electrical sheets of the stator have a predetermined magnetic permeability in this case, depending on the material that is used.
US2011/0316376A1 discloses a radial magnetic bearing comprising an active part which is embodied as a hollow cylindrical stator with teeth and windings that are guided around some of said teeth, wherein three adjacent teeth and the windings guided around said teeth form E-shaped electromagnets in each case. The electromagnets may consist of a cobalt-iron alloy in this case. Provision is also made for wedges at the radial outer edge between the electromagnets and for a housing which accommodates the electromagnets and the wedges, wherein both the wedges and the housing consist of non-magnetic material.
JP 2009 247060 A discloses an electric motor comprising a stator which has stator teeth. In order to suppress undesired high-frequency magnetizing components, the stator teeth of tooth height L have in each case a tooth tip which measures up to L/20 and is made from a material of higher magnetic permeability than the respective remaining stator tooth.